A method for injecting a sealing gel into a recess for a work piece is well known. Generally, this known method includes a step of directly injecting a fluid sealing gel into the recess that is not enclosed and directly exposed the outside, in an open injection manner, especially if the recess is continuously uniform. However, if the recess is not continuously uniform or has a special shape or structure, it is difficult or even impossible to form inject the sealing gel proximate the recess, for example, to form a predetermined structure with a special shaped slot. During an open injection, the fluid sealing gel, injected into the recess, can freely flow into the recess and cannot be constrained to a special shape proximately positioned with the recess. Thereby, it is impossible to form a special shaped slot in such open injection manner. In the prior art, after the sealing gel is directly injected into the recess during open injection, solidified sealing gel needs to be cut and ground a special shaped slot, in order to remove overflowed or excrescent sealing gel. Accordingly, the method in the prior takes much time and effort, and wastes a lot of sealing gel, increasing the cost.